Current transformer



July 12, 1949. J. P. SMITH, JR

CURRENT TRANSFORMER 3 Sheets-Sheet 1 Filed Sept. 11, 1946 FIG.

gwue/wbo b JOHN RSMITH J'R.

July 12, 1949. J. P. SMITH, JR 2,476,121

RRRRRRRRRRRRRRRR ER Filed Sept. 11, 1946 5 Sheets-Sheet 2 July 12, 1949.

Filed Sept. 11, 1946 J. P. SMITH, JR

CURRENT TRANSFORMER 3 Sheets-Sheet 3 Patented July 12, 1949 UNITEDSTATES PATENT OFFICE CURRENT TRANSFORMER John P. Smith, In, Verona, N.J., assignor to Daven Company, Newark, N. J., a corporation of NewJersey Application September 11, 1946, Serial No. 696,136

19 Claims. (01. 175-358) This invention relates to transformers and moreparticularly to a transformer which may be coupled to an inputelectrical circuit without cutting the secondary winding or windings areprotected from attack by moisture or foreign matter in m stances whenthe transformer is subjected to adverse weather conditions includingsalt water spray, or wide variations in climatic temperatures.

More particularly the present invention comprises a transformer of thetype specified which includes a core made up of laminated plates.certain of which are pivotly connected to others in such manner as toprovide inter-engaging leaves, which may be opened to permit insertionof an electrical input circuit wire into the magnetic circuit and thenclosed, the said inter-engaging leaves of the core providing a prongedor interleaved joint which not only will provide relative ease ofopening and closing the Joint but will provide a wiping action inclosing to remove any foreign matter from the leaves or plates andeliminate the interference with the operation of the transformer by suchforeign matter.

A further object of the present invention is to provide a novelconstruction of secondary winding for the transformer whereby thesecondary winding is hermetically sealed without providing a shortcircuited turn of low resistance which would interfere with theoperation of the transformer as well as providing complete protectionfor the secondary winding from moisture, foreign matter. effects of wideclimate temperature changes etc.

Another object of the present invention is to provide a novel manner ofsupporting the transformer coil, so that when the transformer is used inhighly amplified audio circuits short circuits between the coil and itsenclosing housing are prevented, and further to provide a moisture proofseal for the housing when it is closed and in operation.

With these and other objects inview as may appear from the accompanyingspecification, the invention consists of various features ofconstruction, and combination of parts, which will be first described inconnection with the accompanying drawings, showing a transformer of apreferred form embodying the invention, and the features forming theinvention will be specifically pointed out in the claims.

In the drawings:

Figure 1 is a vertical section through the improved transformer.

Figure 2 is a vertical section through the improved transformer taken atright angles to the section shown in Figure 1.

Figure 3 is a perspective view of the openable laminated core showingthe hermeticall sealed secondary coil attached thereto and showing thecore open.

Figure 4 is a perspective view of the openable laminated core withoutthe secondary coil and showing the core open.

Figure 5 is a detail side elevation of the openable laminated coreshowing the core open.

Figure 6 is a vertical section of the stationary part of the openablelaminated core taken on line S--S of Figure 5.

Figure 7 is a view similar to Figure 5 showing the core closed.

Figures 8, 9, and 10 are views in side elevation showing a slightmodification of the openable laminated core.

Figure 11 is a side elevation of a slightly different form of theopenable laminated core.

. Figure 12 is an edge elevation of the core shown in Fi ure 11.

Figure 13 is a perspective view of an insulating sleeve employed in theconstruction of the secondary coil of the transformer.

Figure 14 is an isometric view of the secondary coil enclosed within itscontainer.

Figure 15 is a perspective view of one half of the secondary coilenclosing container.

Figures 16 and 16A are views illustrating the manner of winding thesecondary coil.

Figure 17 is a view of the completed, taped secondary coil.

. Figure 18.is a view of the completed enclosed secondary coil showingits relation to the openable laminated core.

Figure 19 is a view similar to Figure 18 but showing the manner ofattaching the hermetically Sealed secondary coil to the openable core.

. Figure 20 is a perspective view of a slightly modified form of thetransformer, with the cover of its container removed.

To connect the transformer to an electrical input circuit withoutcutting any wire in the circuit the transformer core I is made so thatit may be opened as shown in Figures 4 and 5 of the drawings to permitinsertion of a wire or wires 56 of the input circuit within the core. Topermit this opening of the core, and to facilitate and reduce the costof manufacture of the core I, it is built up of a plurality of plates orleaves.

The lower or stationary section 2 of the core I is built up of aplurality of U-shaped plates 3. One leg 4 of each of the U-shaped plates3 is shorter than the other leg 5. In building up the stationary section2 one or more of the U-shaped plates 3 are placed in flat side wiseengagement with their long legs 5 and their short legs 4 engaging oneanother to form sets. Any desired number of these sets of the U-shapedplates are then arranged in flat sidewise engagement with the long legsof one set lying flat against the short legs of the adjacent set thusforming alternate slots or spaces 8 and projections 'I at the upper endsof the assembled stationary section 2 of the core I. The various plates3 of each set and the setsof plates making up the core I are held inproper assembled position by bolts 8.

The upper moveable section 9 of the core I, is made up of a pluralityotL-shaped plates III, and in building up the moveable section 9 one ormore of the L-shaped plates I are placed in fiat side wise engagement.The same number of L-shaped plates are arranged in each set as thenumber of u-shaped plates 3 in the sets of the stationary section 2, andthe sets are arranged alternately as clearly shown in Figure 4 of thedrawings so as to provide alternate depending prongs II and spaces I2.The L-shaped plates II) are bolted or held together by suitable boltsI3, and the movable section 8 of the core I is pivotly connected to thestationary section 2 by a suitable bolt I4 which extends through theinterengaging prongs or legs III of the L-shaped plates I0 ani legs 5 ofthe U-shaped plates 3, so that when the core I is closed to engage awire of an input electrical circuit, the tree prongs or legs I6 willengage in the spaces 6 formed in the upper end of the outer side of thestationary section 2 as indicated in Figure 5 of the drawmgs.

The outer corners of the prongs or legs I6 of the L-shaped plates II andthe outer corners of the projecting ends of the legs 4 forming thestationary plates 2 are rounded as shown at I1 so as to facilitate thepivotal movement of the movable section 9 and the free and relativelyeasy movement of the prongs or legs l8 into or out of the slots orspaces 6.

The provision of the U-shaped plates 2 and the L-shaped plates III andtheir manner of assembly permits all of the U-shaped plates to beexactly alike as well as all of the L-shaped plates, thus simplifyingand cheapening the cost or manufacture of the core structure.

In the form of the core I shown in Figures 5, 6 and '7 of the drawingsthe pivoting bolt I4 is shown located centrally of the side edges of theplates 2 and III while in the forms shown in Figures 8, 9 and 10 of thedrawings the pivot bolt I3 is shown as off the center of the plates.

By placing the pivot bolts I3 of! center the area 4 is reduced to aminimum, and a joint which is not subject to extreme accuracy of fit orclosing. The joint can be slightly open without appreciably afiectingits reluctance and small particles of foreign material in the bottoms ofthe spaces -6 will not adversely affect its operation as might be thecase in the modified form of core shown in Figures 11 and 12 of thedrawings.

Figures 11 and 12 of the drawings show, diagrammatically a simplifiedmodified form of the openable core structure. In this form of the corethe stationary section 20 of the core is composed of a plurality ofU-shaped members 2| arranged in flat sidewise engagement. The legs 22 ofthe U-shaped members 2I' are all of equal length forming in effect twospaced flat surfaces 23 against whichthe lower surface of the movablesection 24 of the core abuts. The movable section 24 of the core is madeup of a plurality of rectangular strips 25 of flat metal lying in sideto side engagement. The movable section 24 is pivoted at 26 to anysuitable support (not shown) so that it may be swung into open position(as shown in Figure 11) to permit engagement of the core with an inputwire or conductor of an electrical circuit. In this form of the core aswell as in the forms shown in Figures 5, 7, 8, 9 and 10 of the drawingsthe input wire is received in the space between the legs of thestationary section of the core. The input wire is so shown in Figures 1and 2 of the drawings. In the transformers of the present invention itis not satisfactory to pot the secondary coils as specified which willoperate sufiiciently under adverse weather conditions a novelconstruction of hermetically sealed secondary coil is provided. Toprevent short circuiting oi the secondary coil through its containingcan, the wire of which the secondary coil 30 is formed is threadedthrough the longitudinal bore 3| of a glass insulating sleeve 32.

Figure 16 illustrates one manner of threading .the wire through theinsulating sleeve 32, in

which operation a needle 33 (see Figure 16A) having splits 34 in itsends, and on which needle the wire 35 employed for making the coil 30 iswound, is passed a number of times through the insulating sleeve 32until sufllcient wire to form the coil 30 is unwound from the needle 33.

- The coil of wire, forming the coil 30 is then taped in the usualmanner as shown in Figure 17 of the drawings.

The glass insulating 'sleeve 32 has annular bands 36 of metal around itscircumference at each end and these annular metal surfaces provide forsoldered engagement of the sleeve 32 with the sealing can or housing 31which encloses and hermetically seals the secondary coil 30.

The housing 31 is formed of two halves 33,

channeled, as shown at 39 in Figure 15, of the drawings, to receivetherein the coil 30. The halves 38 of the can or housing 31 areapproximately rectangular in shape with a central open portion 40 andthe bottom cross portion of the halves 38 are cut away as shown at H toreceive the glass insulating sleeve. After the coil 30 is placed in thehalves of the housing or can 31,

with the glass insulating sleeve 62 in proper position, the halves aresoldered together and to the metalized ends of the sleeve 32, therebyforming a hermetically sealed housing for the secondary coil 30. Theleads 42 and 43' are brought out through the housing 31 through tightsealing insulators 44, which are preferably of glass, but may be made ofany other suitable sealing insulating material.

The opening 40 in the housing 31 is sufllcient size to permit thesecondary coil assembly to be threaded on the stationary section 2 ofthe coil I as shown in Figures 3, 1 and 2 of the drawings.

When the transformer is employed in highly amplified audio circuits itis necessary to support the secondary coil assembly in such manner thatonly one of the plates 2 of the laminated core I is shorted to the coilassembly. If the coil assembly is permitted to touch or short the core Iat more than one of the plates 2, transients are set up in the windin ofthe secondary coil 30 which interfere with the proper and clearreception of the audio signal.

To provide for proper and secure support of the secondary coil assemblywith contact of only one plate 2 of the core structure a spider or frame45 is provided which is preferably made of brass, and has three lengthsor sides 46, as clearly shown in Figure 19 of the drawings. The two sidearms 46 have ears 41 thereon which are soldered to the housin or can 31as shown at 48. The spider or frame 45 is securely fastened to one sideof the core I with the other sides of the core spaced to provideinsulating air spaces as clearly shown in Figure 19. This constructionnot only eliminates the setting up of transients in the transformer butgives rugged mechanical support to the secondary assembly.

Figures 1 and 2 of the drawings show the core assembly and secondarycoil assembly as applied to the design of an audio pickup.

In this construction the core I and hermetically sealed secondary coilstructure attached thereto are enclosed in a container 50 including amain body 5| and a cover 52 which is hinged at one side, to the body 52as shown at 53.

The secondary coil assembly and the stationary section 2 of the core Iare located in the body 5I and are surrounded by a shield 54 of highpermeability which will minimize the picking up of unwanted audiosignals such as power line hum, etc.

To insure proper operation of the transformer it is necessary to somount it in the container 50 that the pressure on the laminating plates2 of the core will not be so great as to render the opening operation ofthe movable section 9 of the core I too stiff or cause such pressurebetween the plates to produce undesirably increased eddy currents whileat the same time a certain amount of pressure on the plates 2 must beexerted so as to prevent weaving or slipping of the plates 2 and I0 overeach other thus producing unwanted and undesirable noises in the pickup.A too loose mounting also produces mechanical difliculties such asimperfect matching of the prongs I6 with the corresponding spaces 6thereby preventing proper closing of the core I.

To secure the proper pressure on the plates 2 and I0 of the core thecore and coil assembly are supported on two studs 55 and 56. The studs55 and 56 are the same as the bolts or studs 8 shown in Figure 4 of thedrawings and hereinafter referred to, and consequently they extendthrough the core I, and their size is kept as small as practical so thatthe magnetic path through the core will not be unduly restricted.

Sleeves 51 are threaded upon the protruding threaded ends of the studsor bolts 55 and 56 and they receive in their threaded bores outwardly ofthe ends of the studs 55 and 56, the threaded shanks of screws 58.Spacer washers 59 are positioned between the shield 54 and the wall ofthe container 50 and are held in place by the screws 58. Looking washers60 are mountable on the studs or bolts 55 and 56 and engage the coil I.

In assembly the transformer in the container 50 of the sleeve 51 on theright in Figure 1 is threaded on the protruding threaded end of the studor bolt 55 and is soldered to the spider or frame 45 as shown at 6|. Alocking nut 62 is then threaded on thelei't protruding end of the studor bolt 55 against the washer 60 until the desired pressure on theplates 2 is provided. The sleeve on the right is then backed off thestud or bolt 55 until the core and coil assembly fits snugly in properposition within the shield 54. The lock washer 60, lock nut 62 andsleeve 51 at the left in Figure l are then fixed in position bysoldering all three together as indicated at 64. The complete unit isthen assembled using the space washers 59 and screws.

The input wire of an electrical circuit is shown at 65 and it is locatedwithin the opening within the core I when the movable section 6 is inclosed position. The input line wire 65 is held out of contact with thecore I by insulating sleeve 66, carried by suitable supports 61.

A resilient skirt 68, made preferably of synthetic rubber or similarmaterial is carried by the hinged cover 52 and is pinched along theupper edge of the body 5| of the container 50 just above the hinge 53,as clearly shown in Figure 2 of the drawings, thus providingsubstantially water tight joint at this point. The skirt or seal 68 alsoextends through the openings 69 in the cover 52 and engages about thewire 65 adjacent the points where it extends through the openings 69.The skirt 68 further extends downwardly over the connecting jointbetween the free edge of the cover 52 and the body 5| as shown at 16. i

The free edge of the cover 52 has an apron 1I formed thereon whichoverlaps the corresponding upper edge of the body 5| and this apron "IIis perforated to receive a locking button 12. The locking button 12 iscarried by a sprin tongue 13 which in turn is carried by the body 5 I.When the cover 52 is in closed position the looking button 12 will snapinto locking position and hold the cover closed. To release the lockingbutton 12, an operating button 14 is attached to the spring 13 formoving the spring 13 to move the button 12 out of locking position withrespect to the cover 52.

When the cover 52 is closed the interior of the container and thetransformer parts therein will be effectively protected from weatherconditions.

The lead wires 42 and 43 are connected to suitable ports 16 carried bythe container 50.

The construction shown in perspective in Figure 20 of the drawingsdiffers only in minor features from the structure shown in the otherfigures of the drawings, such diflerences consisting mainly in theprovision of insulated holdons for the live wire, the greater cuttingaway or rounding of the comers of the protruding ends of the U-shapedplates and the L-shaped plates as shown at 8| and the changed latchconstrucgamma 7 tionemployedlorholdingthecoverottbecontainerin closedposition.

As shown in Figure 20 the spring tongue or stripllispositionedexterlorlyof thecontaincr SI and has a semi-pyramidallatch block ll carried thereby. This view also clearly shows thesupports 85 for the insulating sleeves G6 which correspondtofliesleevesii,andsti'ipsofinsulation It which prevent contact of alive wire with the supports 05 and container II.

It'will be understood that the invention is nottobelimitedtothespeciflcconstructionorarrangement oipartsshowmhutthattheymaybe widely modified within the invention definedby the claims.

What is claimedis:

1. A split core current transformer comprising, a core including astationary section and a movable section cooperating to provide aconductor receiving passage through an annular magnetic circuit whenclosed. said movable section movable to permit insertion oi. a conductorthrough said passage. a secondary coil assembly including an insulatingsleeve,acoilofwirepasedthroughsaidsleeveinsuchamannerastoformacontinuous open center annular coil withsaid sleeve enclosing one portion of the coil, a substantially horseshoeshaped housing enclos'ng all of said coil except that portion containedwithin said insulating sleeve, said insulatin sleeve being locatedbetweenthelegsofthehousingandbonded to the housing to form ahermetically sealed housingforthewirecoiLtheportionofsaidcoiland housingopponte to said insulating sleeveextendingthroughsaidpasageandmeansforrigidly;

connectin said housing to said core.

2. A split core current transformer as claimed inclaim lincludingacontainerforthecoreand secondaryeoiLandinsulatingmeanscarriedby thecontainer to prevent a conductor which may extend through said passagefrom contacting said core.

3. A split core current transformer as claimed in claim 1 wherein saidcore is made up of a plurality of laminated plates, a container forenclosing said core and secondary coil, means for connecting thestationary section of said core to said container, said means includingmeans to regulate the pressure of the plates of said stationary sectionone the other.

4. A split core current transformer comprising, a core having twoseparable sections cooperating to provide a conductor receivin passagethrough an annular magnetic circuit when con:

nected together, a secondary coil asemhly comprisinganinsulatingsleeve,acoilofwirepassing through said insulating sleeve, a housingenclosingall of said coil except that portion extending through saidinsulating sleeve, said housing having ends abutting and bonded to theends of said insulating sleeve to form a. hermetically sealed enclosurefor said coil, the portionof saidcoil andhousingoppositetosaidinsulating sleeve extending through said passage, andmeans for rigidly connecting said housin to said core.

5. A split core current transformer as claimed in claim 1 including acontainer enclosing said core and coil, and insulating means carried bysaid container to prevent a conductor which may extend through saidpassage from contacting said core.

6. A split core current transformer as claimed in claim 1 wherein saidconnecting means is constructed and arranged to provide contact of thecoilhousingwithsaideoreatonlyonesideotthe core and to provide insulatingair spaces between thecoreandhousingatallotherapproxilnate partsthereof.

'1. Aspiit core current transformer as claimedinclaimlwherelnsaidcoreiscomposedoia plurality of laminated plates, acontainer enclosing said core and coil, means for connecting one sectionof said core to said container, said core and container connecting meansbeing adjustable and constructed and arranged to regulate the pressureof the plates of the core section one against the other.

8. In a transformer for coupling to an input electrical circuit withoutnecessitating the cutting of a wire, a core including a stationarysection and a movable section cooperating to provide a conductorreceiver passage through an annular magnetic circuit when closed, saidmovable section movable to permit insertion of a liveconductorthroughthepasageacoil assembly including an insulating sleeve,a coil of wire passed through said sleeve, a housing enclosing said coiland connected to said sleeve to hermetically seal said secondary coilwithin the housing, a portion of said housing and coil extending throughsaid conductor receiving said core made up of a plurality of plates inflat sidewise engagement, means for rigidly attaching said secondarycoil housing to said core in such manner as to provide contact betweenthe housing and only one plate of said core and provide insulation airspaces between all other parts of the core and housing, a container forenclosing said core and secondary coil, means for connecting said coreand coil to said container, said connecting means extending through andconnecting the plates of said core, and means cooperating with saidconnecting means to regulate the prasure of the plates of the core oneagainst the other.

9. In a transformer for coupling to an input electrical circuit withoutnecessitating the cutting of a wire, a core including a stationarysection and a movable section cooperating to provide a conductorreceiver passage throug an annular magnetic circuit when closed, saidmovable section movable to permit insertion of a live conductor throughthe passage, a secondary coil including an insulating sleeve, a coil ofwire pased through said sleeve, a housing enclosing said coil andconnected to said sleeve to hermetically seal said secondary coil withinthe hous'ng, a portion of said housing and coil extending through saidconductor receiving passage, said core made up of a plurality of platesin flat sidewise engagement, means for rigidly attachingsaidscoilhousingtosaidcoreinsuch manner as to provide contact betwmn thehousing and only one plate of said core and provide insulation airspaces between all other parts of the core and housing, a container forenclosing said core and secondary means for tingsaidcoreandeolltosaidcontainer,saidccnnecting means extending through and connecting theplates of said core, means cooperating with said connecting means toregulate the pressure of the plates of the core one against the other,and insulating means carried by said container for preventing contact ofa live wire with said core.

10. In a transformer for coupling to an input electrical circuit withoutnecessitating the cutting of a wire, a core including a stationarysectionandamovablesectioncooperatingtoprovide a conductor receivingpassage through an annular magnetic circuit when closed, said movablesection movable to permit insertion of a live conductor through thepassage, a secondary coil including an insulating sleeve, a coil of wirepassed through said sleeve, a housing enclosing all of said coil exceptthe portion enclosed in said sleeve, said insulating sleeve connected tosaid housing in such manner as to form a break in the housing, saidhousing and sleeve constructed and arranged to hermetically seal saidsecondary coil within the housing and the insulating sleeve, said coremade up of a plurality of plates in flat sidewise engagement, means forrigidly attaching said secondary coil housing to said core in suchmanner as to provide contact between the housing and only one plate ofsaid core and provide insulation air spaces between all other parts ofthe core and housing, a container for enclosing said core and secondarycoil, means for connecting said core and coil to said container, saidconnecting means extending through and connecting the plates of saidcore, means cooperating with said connecting means to regulate thepressure of the plates of the core one against the other, a cover forsaid container, a resilient moisture proof skirt carried by said coverto protect the interior of the container when the cover is closed, saidskirt extending over the joint between said container and said cover andprovided with openings for receiving therethrough an input wire.

11. In a transformer for coupling to an input electrical circuit withoutnecessitating the cutting of a wire, a core including a stationarysection and a movable section cooperating to provide a conductorreceiver passage through an annular magnetic circuit when closed, saidmovable section movable to permit insertion of a live conductor throughthe passage, a secondary coil assembly including an insulating sleeve, acoil of wire passed through said sleeve, a housing enclosing said coiland connected to said sleeve to hermetically seal said secondary coilwithin the housing, a portion of said housing and coil extending throughsaid conductor receiving passage, said housing rigidly attached to saidcore at only one point to fix the position of said secondary coil tosaid core, said housing being constructed of two halves channeled toreceive the wire coil and provided with curved portions on each half toreceive the ends of said insulating sleeve, said housing halves attachedto each other and to said sleeve at its ends to form a hermetthrough anannular magnetic circuit when connected together, a secondary coilassembly comprising an insulating sleeve, a coil of wire passing throughsaid insulating sleeve, a housing enclosing all of said coil except thatportion extending through said insulating sleeve, said housinghavingends abutting and bonded to the ends of said insulating sleeve to form ahermetically sealed enclosure for said coil, the portion of said coiland housing opposite to said insulating sleeve extending through saidpassage, means for rigidly connecting said housing to said core, andtight sealing insulators carried by said housing at opposite ends ofsaid insulating sleeve, the lead wires of said secondary coil extendingthrough said sealing insulators.

14. A secondary coil assembly for current transformers having an openingtherethrough for cooperative engagement with the core portion of saidtransformers comprising, an insulating sleeve, a coil of wire passingthrough said sleeve in such manner as to form a continuous open centerannular coil with said sleeve enclosing one portion of the coil, asubstantially horseshoe shaped housing enclosing all of said coil exceptthat portion contained within said insulating sleeve, said housin andsaid insulating sleeve ically sealed housing for containing saidsecondall of said coil except that portion contained within saidinsulating sleeve, said insulating sleeve being located between the legsof the housing and bonded to the housing to form a hermetically sealedhousing for the wire coil, the portion of said coil and housing oppositeto said insulating sleeve extending through said passage, and means forrigidly connecting said housing to bonded together to form ahermetically sealed housing for said wire coil. Y

15. A secondary coil assembly for current transformers having an openingtherethrough for cooperative engagement with the core portion of saidtransformers comprising, an insulating sleeve, a coil of wire passingthrough said sleeve in such manner as to form a continuous open centerannular coil with said sleeve enclosing one portion of the coil, asubstantially horseshoe shaped housing enclosing all of said coil exceptthat portion contained within said insulatin sleeve, said housing beingconstructed in two halves and provided with curved portions in each halfto receive the ends of said insulating sleeve, said housing halvesattached to each other and to said sleeves at its ends to form ahermetically sealed housing for containing said secondary coil.

16. A secondary coil assembly for current transformers having an openingtherethrough for cooperative engagement with the core portion of saidtransformers comprising, an insulating sleeve, a coil of wire passingthrough said sleeve in such manner as to form a continuous open centerannular coil with said sleeve enclosing one portion of the coil, asubstantially horseshoe shaped housing enclosing all of said coil exceptthat portion contained within said insulating sleeve, saidhorseshoe-shaped housing having its ends engaging and bonded to the endsof said insulating sleeve to form a hermetically sealed enclosure forsaid coil and tight sealing insulators carried by said housing atopposite ends of said insulating sleeve, the lead wires of saidsecondary coil extending through said sealin insulators.

pa... a...

17. A split core current transformer as claimed in claim 13 including acontainer enclosing said core and coil, and insulating means carried bysaid container to prevent a. conductor which may extend through saidpassage from contacting said core.

18. A split core current transformer as claimed in claim 13 wherein saidhousing and core connecting means are constructed and arranged toprovide contact of said housing with said coreat only one side of thecore and to provide insulating air spaces between the core and housingat all other approximate parts thereof.

19. A split core current transformer as claimed in claim 13 wherein saidcore is composed of a plurality of laminated plates, 8 containerenclosing said core and coil, means for connecting one section of saidcore to said container, said core and container connecting means beingadjustable and constructed and arranged to regulate the pressure of theplates of the core section one against the other.

. 7 JOHN P. SMITH, J1.

REFERENCES CITED.

The following references are of record in the file of this patent:

UNITED STATES PA'I'ENTS Number Name I Date 826,283 Schmidt July 17, 1906854,309 Reed May 21, 1907 1,555,066 Lines Sept. 29, 1925 1,765,913Fischer June 24, 1930 1,935,426 Acly Nov. 14, 1933 2,058,362 SmalleyOct. 20, 1936 2,175,934. Wentz Oct. 10, 1939 2,251,373 Olsson Aug. 5,1941 2,273,534 Mitchell Feb. 17, 1942 2,350,029 Glass, Jr. May 30, 19443,380,300 Gaston July 10, 1945 2,403,340 Camilli 'July 2, 1946 FOREIGNPATENTS Number Country Date 344,575 Great Britain Mar. 12, 1931

